attention to the exploring of the bottom of the sea, commencing with our own coasts, and occasionally extending my excursions to those of neighbouring countries. In laying before the Society some of the results of my investigations, I may be allowed to mention, as an evidence that they have not been altogether fruitless, the fact, that the marine fauna of the Canary Islands had been represented to be of African type, but is proved by me to be much more closely allied to that of the Mediterranean; and, in consequence, the line, marking on a physical map the limit of the tropical fauna, has had to be altered from the north to the south of those islands.

There exists a considerable analogy between the distribution of animals (particularly those which, in consequence of a lower organization, enjoy but very limited power of locomotion,) and of plants. The fauna, as well as flora, of the arctic and antarctic regions being poor in genera and species, but rich in the number of individuals, while the tropics furnish the greatest variety of form in both departments. Also, similar conditions in distant parts of the world present representative, but not identical, species and genera, both in the animal and vegetable kingdoms; and, although the region of Australasia would appear at first sight to form an exception to this rule, a closer observation will shew that its real peculiarity consists in its representing a more ancient state of things, such as may probably have existed in other parts of the world at some period prior to the creation of man.

This view is, I believe, borne out by the general character of the plants and vertebrate animals, whilst among the mollusca may be quoted the characteristic genus Trigonia, not met with elsewhere in a living state, but largely represented in the oolites of this country.

It is well known with respect to land vegetation, that a difference of elevation compensates for difference of latitude, and that arctic forms. are repeated in the same or similar species on the lofty mountains of the temperate and even of the torrid zones. It might be supposed that the analogy would hold good with respect to the marine mollusca, but such is the case only to a very small extent. The temperature of the

ocean, at great depths, being uniform in all latitudes at about 40 degrees of Fahrenheit, it is very evident, that although the inhabitant of shallow seas in temperate regions may, by descending to a greater depth, procure a similar average temperature either in higher or lower latitudes, the same resource would not be available to the natives of

Captain Denham states, that at 200 fathoms it averages 50° and 52°, no matter what the surface temperature may be; and below that depth, diminishes till it reaches the minimum of 40° at 900 to 1000 fathoms.

extreme climates. It is also necessary to bear in mind, that a suitable temperature is not the only condition necessary to the existence of animals, and that at the moderate depth (compared with the height of mountains) of 600 fathoms, there must exist total darkness, and a pressure equal to 120 times that of our atmosphere, or about 1800 pounds to the square inch; a state of things which we cannot imagine to be very convenient, even if it be not absolutely opposed, to animal existence.

As the depths of the sea are influenced by climate in an inverse ratio to their distance from the surface, till the point of an unvarying temperature is reached, it is evident that difference of latitude must be of much less importance to those beings which inhabit the deep sea, than to shallow water species, and we accordingly find the former to be more extensively distributed than the latter. A considerable variation, as regards the distribution of mollusca, takes place between the opposite sides of the north Atlantic. On the eastern shores, intervening between those of the arctic and tropical regions, are two distinct faunas, which have been termed the Celtic, and the Lusitanian or Mediterranean; and these so run into one another, that it would be difficult to fix upon an exact line as the commencement or termination of either of them. On the American shores, species generally characteristic of the arctic seas extend southward as far as Cape Cod in lat. 42° (the parallel of the north of Portugal), where they are said to disappear abruptly, and to be replaced by genera including Pyrula, Ranella, and Columbella, evidently forms of a more southern type, and which appear to represent those constituting the Lusitanian fauna on this side of the Atlantic.

Dr. Philippi has appended to his admirable work, on the Mollusca of Sicily, a comparison of the fauna of that country with the faunas of all the principal districts and localities of which there had been any list of shells published. I have considered that it would not be uninstructive to follow his example within a narrower sphere, by comparing together the shells of those parts which I have personally examined and some others of a similar character, with a view of illustrating the range of northern species southward, and likewise of southern species towards the north. I commence with

WESTERN SCANDINAVIA.

In a catalogue of the Mollusca of Western Scandinavia, published by Professor Lovén, of Stockholm, there are, after rejecting a few

which prove to be synonyms, 289 species provided with shells, consisting of

Of these the following are found in North America, being taken principally from Dr. Gould's catalogue of the Mollusca of Massachusetts :

Total of testaceous mollusca, common to Western Scandinavia and North America, 58 in 289, or 20 per cent. of the former.

The Scandinavian species found in the British seas are

Total of testaceous mollusca, common to the west of Scandinavia and the British seas, 217 in 289, or 75 per cent. of the former.

The Scandinavian species found on the north coasts of Spain, including Vigo, are the following.-N.B. Some of them which I have not actually procured within the district, are included in consequence of their having been met with further south, and these are distinguished by the addition of their locality:—